Clown Pleco
They stay pretty small, about 4 inches. They need wood in their diet so a piece of driftwood or bogwood is necessary. I think they may eat some algae, but they aren't as great at eating it as bristlenose plecs. They are quite cute if you ask me.

I don't know that I'd get one specifically for algae though, but if you are looking for a small pleco/bottom feeder, a Clown pleco would be perfect. I've never kept one though so I can't be sure on the algae issue.